Currently available devices (referred to as occupancy sensors, motion sensors, automatic wall switch, or the like) are typically designed to replace traditional ceiling light wall switches or switches for other apparatuses. For example, these devices (as exemplified by a schematics shown in FIG. 1) include a lighting controller and a motion sensor that senses the presence of an occupant or a subject within a space to be illuminated by the controlled light. These traditional devices turn on a controlled light immediately upon detecting motion within a monitored space and will subsequently turn off the controlled light following a preset period of no detected motion.
Examples of such devices include: Leviton® PR180-1LW Decora® Passive Infrared Wall Switch Occupancy Sensor, SensorSwitch Wall Switch Decorator Sensor—Passive Infrared (PIR), Watt Stopper® WS-200 Automatic Wall Switch.
The limitations of some of the existing technologies include the method used to determine when to turn the controlled light off. For example, consider a case when a controlled light in a room is lit and a room occupant is sitting in the room quietly reading or resting. If the magnitude of occupant's movements is insufficient to be detected by the motion sensor, the lighting controller will turn off the controlled light following a preset or pre-determined delay built-into the lighting controller. In this situation, the occupant will be left in a darkened room unintentionally.
At least another example of unintentional consequences is an application of the existing technology in a public restroom. An occupant in a toilet stall could get caught in a darkened restroom if s/he remains in the restroom too long, and the occupant may not have any means to turn the lights back on. To use the device under the current technology presents a safety hazard in certain situations, and not using such a device overlooks the energy saving benefits offered by such device.
Furthermore, current technologies that only rely on the preset or pre-determined time delay (without detecting any motion) before turning off the device lacks flexibility unintentionally wasting energy use. For example, suppose the time delay is set to 30 minutes. If a subject approaches the monitored space just enough to trigger the device but immediately moves away from the monitored space, the current technology would unintentionally leave the device on for the full duration of the time delay even though there is no need for the device to be activated or energized.
Moreover, currently available systems are ineffective at positively identifying whether a monitored space is occupied.